A casting apparatus generally comprises an upright casting mold into which the molten metal to be cast is poured from a ladle into the top. The melt forms a stream running from the outlet of the ladle to the body of the solidifying melt within the casting mold.
It is known to protect the casting stream, i.e., the stream of molten metal of a casting installation, before it enters the mold with an inert protective gas which is intended to form a sheath around the stream and thereby prevent oxidation of the molten metal and other undesirable gas takeup. The inert protective gas can be supplied in liquefied form or in gaseous form and generally is nitrogen.
Operating with liquefied nitrogen involves high apparatus costs since it is generally necessary to apply the liquiefied nitrogen directly, i.e., in its liquid state, to the melt.
In such systems, streams of liquefied nitrogen are trained against the casting stream and evaporated upon contact with the molten metal. This system has the disadvantage that the evaporation process produces a mist, cloud or the like which obscures observation of the stream of liquefied metal so that an optical evaluation of the progress of the casting process is not possible.
When gaseous nitrogen is supplied as the stream-surrounding blanket, the apparatus is simpler and less costly and the nitrogen consumption is reduced. However, the gas distributors used for forming the nitrogen blanket around the stream and generally comprised of tubes which completely enclose or surround the stream over its entire length in order to apply a uniform and continuous sheath or blanket of the protective gas. Such tubes, of course, also obscure the molten metal stream so as to prevent a visual determination of the progress of the casting process.
Both of these prior-art systems, moreover, have a common disadvantage in that spattered droplets from the molten metal stream become fixed to the gas or liquid distributors and eventually obscure the respective outlets on the sides of the distributors turned toward the molten stream. This of course has the disadvantage that it may interrupt the formation of the protective sheath of inert gas or cause partial disruption thereof with all of the drawbacks involved in the casting with an unprotected stream. Of course, when the surface of the distributor turned toward the molten metal stream is completely coated with droplets of the molten metal, all supply of the protective gas is terminated.